My long-term career goal is to elucidate the cellular and molecular basis governing the maintenance and function of neural circuits under physiological and pathological conditions. To understand how the nervous system copes with injury thus offers a unique opportunity to tap into these questions and defines the objective of this proposal-to identify and delineate novel factors regulating axon regeneration, and develop effective strategies to promote axon regeneration based on these new targets. To lay a solid foundation for achieving this goal, I joined the laboratory of Dr. Yuh Nung Jan, a world-renowned pioneer in studying neural circuits assembly and function. I initiated my postdoctoral research by establishing a Drosophila sensory neuron injury model that resembles the mammalian injury model at the phenotypical and molecular level, to screen for novel regulators of axon regeneration. My studies have already led to the identification of the RNA processing enzyme Rtca as an inhibitory factor for axon regeneration in the central nervous system (CNS). Successful completion of the proposed studies will validate the novel concept of targeting the Rtca pathway in treating neural injury and neurodegenerative diseases, and spur my future independent research to uncover the repertoire of molecules governing regeneration. Damage to the adult CNS, such as spinal cord injury (SCI) often leads to persistent deficits due to the inability of mature axons to regenerate after injury. Under pathological situations such as multiple sclerosis (MS), the second most common neurological disorder leading to disability in young adults, the failure of damaged axons to regenerate contributes to non-reversible neurologic dysfunction. Currently, only a few therapies with limited efficacy are available, highlighting the urgent need to identify novel molecular targets and develop targeted therapies. To this end, I have focused my postdoctoral research on building a platform to take advantages of the power of fly genetics in discovering novel factors together with the mammalian injury model to study their homologs and functional recovery. I propose two directions to go after the regeneration regulators: in specific aim 1, I will determine the interplay between axon degeneration and regeneration, test the hypothesis that perturbing degeneration delays regeneration; in specific aims 2 and 3, I will determine the mechanisms underlying dRtca/Rtca's regulation on axon regeneration using fly and mouse injury models, and test the hypothesis that removal of dRtca/Rtca enhances circuit reassembly and functional recovery. My extensive study has already resulted in a recent first author publication in Genes and Development in 2012 (cover article), with two co-first author papers in revision in Neuron and Nat Neurosci. I have generated many novel reagents (e.g. the Drosophila injury model, transgenic and knockout fly strains, and knockout mice), and assembled an extraordinary advisory team consisting of co-mentors (Dr. Michael S. Beattie, Professor in Residence of Neurological Surgery at UCSF, Director of Research of UCSF Brain and Spinal Injury Center (BASIC); Dr. Jacqueline C. Bresnahan, Professor of Neurological Surgery at UCSF and President of the National Neurotrauma Society), and consultant (Dr. Jonathan S. Weissman, Professor of Cellular Pharmacology and Biochemistry at UCSF, an HHMI investigator and a member of the National Academy of Science). I have also established close collaborations with members of the BASIC at UCSF, which specializes in animal models of brain and spinal cord injury. The culture of BASIC is highly collaborative, and includes both basic and clinical research projects in neurotrauma. I am therefore uniquely poised to undertake the novel studies proposed in this application with great translational potential. Research proposed in my K99 mentored phase (year 1 and 2) is mainly focused on studying the regulation of axon regeneration by degeneration and dRtca in flies, as well as establishing the mice injury model. I will carry out these proposed experiments with the supervision of Dr. Yuh Nung Jan and support from my advisory team. In the R00 independent phase (year 3 to 5), I will focus on characterizing the roles of four new factors, which came out from my degeneration screen, in modulating regeneration in flies, as well as studying the function of Rtca in regulating regeneration in mice, with the continual support from my advisory/collaborative team. At the completion of this project I expect to have (1) established mechanistic links between axon degeneration and regeneration, (2) determined the molecular mechanisms of how removal of dRtca/Rtca promotes CNS axon regeneration in flies and mice, and (3) identified additional new regulators of axon degeneration/regeneration. My proposed research is highly innovative because our knowledge of the underlying mechanisms is still far from complete for axon degeneration/regeneration, and my studies will bring in new approaches to systematically uncover novel regulators, with the potential to provide new therapeutic targets. With a Ph.D. background in developmental neurobiology, and postdoctoral training in bioinformatics, mouse genetics and surgery, I possess a unique skillset and hence am in a highly advantageous position to accomplish the proposed novel studies. Dr. Jan has extended his full support towards my career goals and has encouraged me to take these projects to my independent lab in the future. The proposed studies build logically on my prior and ongoing works as evidenced by my recent publication, and will undoubtedly prepare me to lead a novel and strong independent research program in the near future.